Is Boeing's 787 safe to fly?

Yesterday, Boeing (BA) announced its fifth delay in the delivery of its latest aircraft, the 787 Dreamliner. Boeing has 865 orders for the $178 million aircraft, which is designed to cost 20 percent less to operate and maintain. A big reason for these savings is the 787's use of composite materials -- for example, All Nippon Airways, which is to be first to receive the 787, said in April that fuel savings and higher revenue from the higher capacity 787 could add $100 million in fiscal 2011.

But the very composite materials that are saving money for airlines are now contributing to the problems that delayed the 787 for the fifth time. And those problems raise questions about whether it can ever be safe to fly -- which would probably scare passengers from boarding the 787.

In order to understand why the 787 might be unsafe, it is crucial to understand more about the 787's composite materials -- including carbon fiber reinforced epoxy tape. Older aircraft are made of aluminum, which is heavier than the composite material.

Composites are lighter and stronger hence able to fly more fuel efficiently. But engineers don't completely understand how aircraft made of composite materials will respond to the stresses of actual flight. This incomplete understanding is reflected in the computer models they use to design the aircraft. The reason for the fifth delay is that the actual 787 did not behave the way the model predicted.

Specifically, Boeing found that portions of the airframe -- those where the top of the wings join the fuselage -- experienced greater strain than computer models had predicted. Boeing could take months to fix the 787 design, run more ground tests and adjust computer models to better reflect reality.

And this is what raises questions about the 787's safety. If engineers continue to be surprised by the 787's response to real-world operating stresses, there is some possibility that the testing process might not catch all the potential problems with the design and construction of the aircraft.

Moreover, the Federal Aviation Administration (FAA) has already recognized that composite materials require new methods of inspection for cracks. Maintenance personnel inspect metal aircraft for cracks through visual inspection. However, several weeks ago the FAA recommended X-ray and ultrasound inspection of carbon-reinforced plastic rudders on Airbus A-330 and A340 aircraft.

The 787 is a major technological innovation and Boeing will work diligently to protect its reputation for safety and quality in developing that innovation. But the difficulty Boeing engineers are encountering in predicting how the 787 responds to real-world stresses, as well as the new maintenance challenges the 787 would need to overcome, raise deep safety questions.

Let's hope that passengers don't find themselves on the bleeding edge of the 787's innovation.